Bidirectional electronically scanned antenna system



P. SAFRAN 3,430,242

BIDIRECTI ONAL ELECTRONICALLY SCANNED ANTENNA SYSTEM Filed Dec. 5, 1967 FIGS - FIGJ FIG-'4 FIGS Macaw m2:

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BIDIRECTIONAL ELECTRONICALLY SCANNED ANTENNA SYSTEM Filed Dec. 5, 1967 1 Sheet 2 of s Fl(3.3v

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Feb. 25, 1969 P. SAFRAN 3,430,242

BIDIR ELCTIONAL ELECTRONICALLY SCANNED ANTENNA SYSTEM Filed Dec. 5, 1967 Sheet 3 of :5

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8 Claims ABSTRACT OF THE DISCLOSURE A transmission lens phased array. Two feed assemblies, one on each side of the lens, form antenna beams simultaneously or sequentially, using the same lens, phase shifters and drivers. Two arrays oriented at 90 from each other scan 360.

Background of the invention This invention relates to, electronically scanned antenna systems, and in particular to a planar, linear or other configuration antenna system for forming antenna beams on both of two sides of an electronically scanned antenna. It has particular, but not exclusive, application to radar systems for scanning 360 in azimuth.

Illustrative examples of conventional electronically scanned antennas and their modes of operation are shown and described in Sperry Engineering Review, Winter, 1965, and in Boeing Document D2-82590-1, and in the references cited therein.

The use of electronically scanned radar antennas, rather than mechanical antennas, has been dictated by modern size, weight, data rate, and flexibility requirements in an increasing number of applications.

One of the objects of this invention is to provide an electronically scanned antenna system which requires less prime power and which is cheaper, lighter, and less complex than presently known antenna systems.

Other objects will become apparent to those skilled in the art in the light of the following disclosure and accompanying drawing.

Summary of the invention In accordance with this invention, generally stated, an electronically scanned antenna system is provided in which radiating elements adapted to form antenna beams are provided on both sides of a single phased array lens antenna. In the preferred embodiment the phased array antenna comprises a cellular structure of phase shifters activated by drivers controlled by a beam steering computer. The phase shifters may be either ferrites or diodes, digital 'or analog, reciprocal or non-reciprocal. Also in the preferred embodiment, the lens is of the transmission type and has optical feed systems on both sides of the lens. Each feed system thus energizes radiating elements on the side of the lens opposite it.

The lens faces may be planar, linear, or other configuration, and are preferably mirror images. The term planar is used herein to indicate any such configuration.

If each array is capable of scanning :45 in azimuth, the antenna system of this invention allows scanning a full 360 in azimuth with only two arrays, rather than the four required with presently known antenna systems.

Brief description of the drawing In the drawing, FIGURE 1 is a diagrammatic view of one embodiment of antenna system of this invention, having reciprocal phase shifters in the antenna array;

FIGURE 2 is a somewhat diagrammatic view in perspective of the antenna system shown in FIGURE 1;

nited States Patent ice FIGURE 3 is a diagrammatic view of the antenna system shown in FIGURE 1, in use in a radar system;

FIGURE 4 is a diagrammatic view in top plan of two of the antenna systems shown in FIGURE 1, arranged to scan 360 in azimuth;

FIGURE 5 is a view in perspective of the two antenna systems shown in FIGURE 4;

FIGURE 6 is a diagrammatic view of another embodiment of antenna system of this invention, having nonreciprocal phase shifters in the antenna array; and

FIGURE 7 is a diagrammatic view of another embodiment of antenna system of this invention.

Description of the preferred embodiment Referring now to the drawings, and particularly to FIG- URES 1, 2, 3, and 5, reference numeral 1 indicates one illustrative embodiment of antenna system of this invention. The antenna system 1 includes a transmission type lens 2 containing a large number of reciprocal phase shifters 3 supported by a cellular structure. Radiating elements 4 and 5 on opposite faces 6 and 7 of the lens 2, respectively, are operatively connected to the phase shifters 3. The radiating elements 4 and 5 are respectively energized by feed horns 8 and 9 on the opposite sides of the lens 2 from the radiating elements 4 and 5. As shown in FIGURE 5, the feed horns 8 and 9 may be offset from the central axis ofthe lens 2, to minimize aperture blockage. When the feed horn 8 is energized, the radiating elements 5 act as collectors, which feed the radiating elements 4 through the phase shifters 3 and thereby form an antenna beam 10 in a direction normal to a phase taper 12 induced by the phase shifters 3. Likewise, when the feed horn 9 is energized the radiating elements 4 act as collectors, which feed the radiating elements 5 through the phase shifters 3 and thereby form an antenna beam 11 in a direction normal to a phase taper 13 induced by the phase shifters 3. The phase tapers 12 and 13 are controlled in the usual manner by adjusting the phase shift induced by each phase shifter. This function is usually performed by drivers 14 controlled by a beam steering computer 15. The phase shifters are generally set to convert the spherical wave fronts from the feed horns 8 and 9 to planar phase fronts, but the computer-controlled drivers may set the phase shifters to vary the beam shape by forming a non-planar phase front. Because reciprocal phase shifters introduce the same phase shift regardless of which way power passes through them, the phase tapers 12 and 13 will be oriented as mirror images with respect to the lens 2.

It will be seen that because optically fed transmission type electronically scanned antenna lenses generally have collectors on the feed horn side which are identical with the radiating elements on the opposite side, the lens de scribed is precisely identical with that used in a standard antenna of this type.

The feed horns 8 and 9 may be turned on simultaneously or sequentially. If they are turned on simultaneously, reception will also be simultaneous, if range to target is equal for both beams 10 and 11. When a target is detected, its direction is easily determinable from which feed 8 or 9 receives the signal if separate receivers 17 are used, or by temporarily turning off one feed if a single receiver 17 is used. One feed may also be turned off when a tracking mode is used, to conserve power.

As shown in FIGURE 3, a radar system using the antenna system of this invention may be of a conventional type, with each feed 8 and 9 and the phase shifters 3 controlled by the computer 15, and with a transmitter 16 and receiver 17 connected to the feeds through a duplexer 18.

A second embodiment 101 of antenna system of this invention is shown in FIGURE 6. The system 101 is identical with the embodiment shown in FIGURE 1 except that the phase shifters 103 are non-reciprocal. Therefore, the phase tapers 112 and 113 are generated parallel to each other rather than being mirror images. This embodiment suffers from the drawback, not present in the embodiment shown in FIGURE 1, that the path length compensation which must always be made for a spherical phase front propagated from the feed cannot be accomplished in both directions by means of the non-reciprocal phase shifter settings, and hence must be achieved by providing cumbersome line lengths in the lens array, with the longest lengths in the center of the lens.

The lens may also be of the reflection type, as shown in FIGURE 7, with two polarized feed horns 208 and 209 and two polarized shorting planes 219 and 220. Each shorting plane reflects the phase front from the opposite horn but passes that from the adjacent horn. Thus, beams 210 and 211 are formed on the same sides of the lens as their generating feed horns 208 and 209. Reciprocal phase shifters 203 must of course be used.

In order to scan 360 in azimuth, it is only necessary to use two of the antenna systems of this invention, placed at right angles. As shown in FIGURES 4 and 5, one antenna may be placed above the other. For scanning, a single computer for both lenses is suflicient. For almost all applications, two computers, one for each lens, are sufficient. This array will give full 360 coverage with each side of each lens giving :45" scan capability. If ordinary antenna systems having 145 scan capability are used, four antenna systems including four arrays of phase shifters with drivers would be required. By requiring only two arrays of phase shifters with drivers, the antenna system of this invention halves the expense of two of the most costly components of such a system. The size, weight, complexity and prime power requirement of the system are also approximately halved.

Monopulsing and multimoding may be accomplished with the antenna system of this invention by standard methods.

Numerous variations in the antenna system of this invention, within the scope of the appended claims, will become apparent to those skilled in the art. As has been seen, the phase shifters may be either reciprocal or nonreciprocal, may be ferrite, diode or other type, and may be digital or analog. The feed may be a confined feed rather than an optical feed. In this case, however, extreme care must be taken to avoid severe aperture blockage. These variations are merely illustrative.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In an electronically scanned lens antenna having a pair of oppositely disposed faces, the improvement comprising a set of radiating elements on each of said faces, said sets of radiating elements being adapted to form antenna beams when energized, and a feed system means for energizing said sets of radiating elements.

2. The antenna of claim 1 further comprising a second electronically scanned lens antenna having a pair of oppositely disposed faces and having a set of radiating elements on each of said faces and a feed system means for energizing said sets of radiating elements, said second lens antenna being disposed above and at right angles to the first lens antenna. 2

3. An electronically scanned lens antenna comprising an array of phase shifters, a driver system for controlling said phase shifters, and a plurality of feed systems adapted to transmit electromagnetic waves to said phase shifters, at least one of said feed systems being positioned on a different side of said array from another of said feed systems.

4. The antenna of claim 3 wherein the array of phase shifters is planar and a feed system is provided on each planar side of said array.

5. The antenna of claim 4 wherein the feed systems are optical feeds.

6. The antenna of claim 4 including radiating elements in both sides of said array, each of said radiating elements being energized through a phase shifter by a feed system on the side of said array opposite said radiating element.

7. The antenna of claim 4 including radiating elements in both sides of said array, each of said radiating elements being energized through a phase shifter by a feed system on the side of said array adjacent said radiating element.

8. The method of sending and receiving antenna beams comprising forming beams on opposite sides of an electronically scanned lens antenna.

References Cited UNITED STATES PATENTS 3,305,867 2/1967 Miccioli et al 343- X RODNEY D. BENNETT, Primary Examiner.

T. H. TUBBESING, Assistant Examiner.

US. Cl. X.R. 343754 

